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PROXIMITY OPERATIONS [[underlined]]

On the initial approach to Solar Maximum Satellite, the Orbiter was slowed to 0.2 fps at 250 feet. Low Z was selected at 200 feet. Final braking was initiated with the intent of parking the Orbiter between 150 and 200 feet on the V-BAR and stationkeeping during the orbit night phase. At this time, the Solar Maximum Satellite was approximately 2 degrees high in the COAS. The closure rated could be eliminated but within a very short time the attitude corrections, which were automatically responding to deadband excursions, would reinitiate a closure rate or 0.2 fps.

Attitude control was maintained with NORM jets during this period because VERN jets had demonstrated this closure problem with low Z NORM jets but not to the degree experienced during flight.

Range continued to decrease and extreme jet braking activity proved ineffective in stopping the closure rate. Finally, at 80 feet, the Solar Maximum Satellite was moved to 8 degrees high in the COAS to try and use the orbital mechanics effect of having the Orbiter center of gravity (CG)  well below the Solar Maximum Satellite to produce an opening rate. This worked with some degree of success and the Orbiter was backed out to 140 feet. However, the closure rate started again at a very slow rate. As a result of this exercise, the low Z control mode was not considered a viable stationkeeping mode (R).

With the Orbiter's lighting configuration, 250 feet was considered the maximum stationkeeping distance during orbital night. For some payloads, 250 feet may be too close for NORM jet activity without low Z. If a requirement exists to stationkeep during night periods outside of 250 feet, better Orbiter exterior lighting should be provided or stationkeeping may not be a viable option (R). It should also be pointed out that lighting was adequate for a comfortable approach and grapple during the orbital night period as long as the range was less than 250 feet at sunset.

Trajectories with low Beta angles, where the sun's path comes very close to the target, which was the case for the Solar Maximum Satellite, were a difficult visual situation. It was important during stationkeeping to be in as stable a situation as possible because it was extremely painful to try and observe the target with the sun in the crews' eyes. The radar range and range rate helped for the opening/closing rates, but the line-of-sight meter was too noisy to be useful, hence there was no way to reasonably make up for the loss of visual tracking for up/down and left/right motion.

After the back out and second rendezvous, the final approach was made with no intent to stationkeep. The Orbiter was again slowed to 0.2 fps at 250 feet on the V-BAR and low Z was selected at 200 feet. To avoid the sun interference problem, inertial attitude hold was selected about 15 degrees earlier than the "end-on" approach that had been practiced in simulations for rotating grapples. This totally eliminated the sun problem and proved not to hamper the grapple operations.

To insure proper braking, low Z was deselected at approximately 80 feet with the Solar Maximum Satellite over the payload bay where plume impingenment did not appear to be a problem. A small amount of rippling of the Mylar on the satellite was noted but no attitude changes were observed due to the jet firings. The Solar